The invention relates to a steering wheel for motor vehicles. In particular, a steering wheel that includes a switching device for actuating an electric functional group of a motor vehicle.
It is customary, in order to trigger electric functional groups of a motor vehicle, in particular to trigger a signal horn, to use one or more switching devices which can be actuated by a force being exerted on a central region of the steering wheel and which in each case comprise two electric contact elements (for example, in the form of contact elements made of silver) which are moveable relative to one another and which can be brought into contact with one another in order to trigger the corresponding electric functional group.
In a switching device of this type, there is the problem that the contact elements in time become contaminated or covered with an oxide layer, this being detrimental to the functioning capacity of the switching device. This applies particularly when, the switching device is used to activate a relay or to transmit a control signal to an electronic device in order to trigger the signal horn device. In these cases, only weak currents with a current intensity of the order of magnitude of 20 mA, along with a voltage of the order of magnitude of 5 V to 12 V, flow across the two contact elements of the switching device.
The contamination or oxidation of the contact elements then has a particularly adverse effect.
An object of the present invention is to provide a steering wheel for a motor vehicle, the steering wheel comprising a switching device for actuating an electric functional group of a motor vehicle and being distinguished by increased functional reliability.
According to an embodiment of the present invention, a steering wheel is provided that includes a switching device having a pair of contact elements. At least one of the contact elements is mounted resiliently so that it slides along the other contact element after the two contact elements have been brought into contact with one another under the force applied in order to make electric contact and close the switching device.
Since, by virtue of the resilient mounting of one contact element, after electric contact has been made the two contact elements execute a relative movement in relation to one another with their contact faces which are in contact, the contact elements are cleaned of contamination and/or freed of an oxide layer. During the closing of the switching device, therefore, a cleaning of the contacts takes place automatically as one contact face slidingly contacts the other contact face.
According to another embodiment of the present invention, the steering wheel is arranged so that when a force is exerted on the actuating portion on the steering wheel, for example in the central steering wheel region, the two contact elements move toward one another along a first direction until they come into contact with one another, and, after contact has been made, the resiliently mounted contact element to yield along a second direction and at the same time slide over the other contact element, the second direction preferably running essentially perpendicularly to the first direction. The contact faces of the two contact element extend essentially perpendicularly to the first direction along which the two contacts can be moved toward one another.
According to an embodiment of the present invention, the two contact elements of the switching device are fastened to two carrying subassemblies of the steering wheel which are moveable relative to one another in order to make contact. In one embodiment, one of the contact elements is secured to a subassembly of the steering wheel skeleton and the other contact element is mounted on a subassembly moveable with respect to the steering wheel skeleton.
According to an embodiment of the present invention, the subassembly is moveable with respect to the steering wheel, preferably comprises a contact carrier and is connected resiliently to the steering skeleton by an elastic element.
The contact carrier provided with one contact element is moved toward the subassembly provided with the other contact element and located on the steering wheel skeleton side, by a force being exerted on the central steering wheel region, in which an airbag module is mounted moveably, so that the two contact elements come into contact with one another.
The resiliently mounted contact element may be connected via an elastic element to the associated carrying subassembly, for example the contact carrier. The elastic element both may be integrally formed in one piece on the contact element and may be produced as a separate elastic element fastened to the contact element.
According to an embodiment of the present invention, the elastic element is placed under prestress in order to ensure a defined position of the contact element and consequently also a defined distance from the other contact element.
In another embodiment of the present invention, the elastic element has a limb running at an acute angle to the direction of movement along which the two contact elements can be brought into contact with one another. The acute angle is selected so that the angle between the limb of the elastic element and the contact face of the contact element is at least 45 degrees. The size of the angle between the limb of the elastic element and the contact face of the associated contact element establishes how far the resiliently mounted contact element moves along the other contact element after the two contact elements have come into contact, when this movement is caused by a defined force.
The associated contact element is fastened to one end of the limb of the elastic element and the other end of the limb is secured to the corresponding carrying subassembly, for example the contact carrier. At the same time, the limb is preferably supported on a supporting element of the carrying subassembly, and this subassembly, on the one hand may be integrally formed in one piece on the limb or, alternatively, forms an inclined plane on which the limb of the elastic element comes to bear.
In order to make it easier to convert a force under which the two contact elements first move toward one another until they are in contact with one another, into a movement during which the contact face of one contact element slides over the contact face of the other contact element, the limb of the elastic element is mounted, preferably with its end facing away from the contact element, at a bearing point of punctiform cross section, so that the limb can pivot.
Furthermore, stops may be provided, which cooperate in order to limit the movement of the two contact elements relative to one another and consequently also to limit the maximum force which the two contact elements exert on one another. The distance between the two contact elements in the direction of movement is smaller than the distance between the two stops along this direction, because the two stops must allow the two contact elements to come into contact with one another and subsequently move parallel to one another, before further movement is prevented by the two stops meeting one another.
According to yet another embodiment of the present invention, the contact carrier comprises a conducting material and is connected to a junction plug, so that the contact carrier can be brought to a defined electric potential. In this case, the contact carrier may also be produced in one piece with the junction plug. The contact carrier and the junction plug, integrally formed in one piece on the latter in order to minimize the contact resistance, may comprise, for example, tinned sheet steel or sheet brass.
In order to prevent the contamination of the contact elements as far as possible from the outset, these may be surrounded by a sheath.
The non-resiliently mounted contact is preferably a contact rivet which has a rough contact face, for example a grooved surface. The rough surface improves the cleaning action which occurs while one contact face is moving along the other. As a result of the rough surface, the contact pressure which has to be exerted by the resiliently mounted contact element on the other contact element in order to achieve a sufficient cleaning action is reduced. Also, the size of the elastic element (e.g., contact spring) used in the resilient mounting of one contact element can thereby be reduced.
According to a further embodiment of the present invention, the resiliently mounted contact element may preferably be formed by a contact plate which has stiffening ribs and/or relief slots or bores, in order to increase or reduce in a specific way the contact pressure which occurs when the two contact elements come into contact with one another under the action of a defined force.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.